1. Field of The Invention
The invention generally relates to four wire to two wire adaptors and, in particular, a two wire adaptive system for use in place of a four wire system for controlling a heating/cooling system.
2. Description of The Prior Art
Forced air central heating and cooling systems for domestic use generally use common ductwork for both warm and cool air. A typical heat-only system is shown in FIG. 1 while a system that provides both heat and air conditioning is shown in FIG. 2.
In a heat-only system of FIG. 1, the room thermostat 10 is simply a temperature-controlled switch that enables electric current to flow to the heat control 20 of furnace 30. The heat control 20 activates the fan 32 and combustion chamber 31 so that fan 32 forces air over heat exchanger 33 and the air temperature is increased. Therefore, only two wires 21 and 22 are required for the connection between the furnace 30 and thermostat 10.
When air-conditioning is added as shown in FIG. 2, a more complex thermostat 100 must be used to contact the heat/cool system 130. The thermostat 100 is a temperature controlled switch with multiple contacts. Electric current flows through the thermostat contacts 100 to the heat/cool control 120. In addition, all heating/cooling systems have a separate, manually-controlled switch F on the thermostat 100 that enables the homeowner to have the fan 132 run continuously for constant circulation air. Therefore, heating/cooling systems require four wires 121, 122, 123, 124 to be run between the thermostat 100 and control 120.
During heating cycles, control 120 activates fan 132 and the combustion chamber 131 so that fan 132 forces air over heat exchanger 133 and the air temperature is increased. During cooling cycles, control 120 activates fan 132 and compressor/condenser 140 so that fan 132 forces air over evaporator 141 and the air temperature is decreased. Essentially, such systems require additional wirees 123 and 124 to respond to cooling switch C and fan switch F.
Many older homes were constructed with heat-only systems that have two wires for interconnecting the control systems of the heating plant with the thermostats shown in FIG. 1. As time passes, the owners of these homes wish to add central air conditioning. Installation of central air-conditioning requires two additional wires 123, 124 to be run between the control system and thermostat as shown in FIG. 2. In many homes with finished basements or thermostat wiring that is hidden behind finished walls, it is very difficult, time-consuming and expensive to run the additional wires.